Prevention or inhibiting of ice accumulations



Patented Dec. 2, 1947 UNITED PREVENTION OR INHIBITIING OF "ICEACCUMULATIONS 'Walter E. Palmer, Eair :Lawmfl.

No Drawing. Application May. 1*1, 1j944, Serial No. 535,202

1 Claim. 1

This invention relates to the treatment .of 'surifacestexposed tomoisture under freezing conditions and to the prevention .of theaccumulation of ice or frost on such surfaces. The surfaces treated :maythe the windshield of a vehicle such as an automobile, the windows ofbuildings, vehicles or other structures, the propeller blades of anaircraft or of various other types.

Formation of ice on propeller blades is particularly dangerous, aspieces of ice breaking off are projected at high speed like missiles,and leave the propeller out of balance. Ice formations on windows,Windshields, etc., destroy or reduce visibility therethrough.

Many compositions have been pro-posed for this purpose, but none withwhich I am familiar are entirely satisfactory. Some are water-soluble sothat they have short life and areoften washed off before the need forde-icing or preventing of ice formation occurs.

Other compositions are translucent rather than transparent and interferewith free vision through the protected glass. To continuously supply acompound to the surface to be protected is wasteful, and uniformdistribution is difficult, if not impossible, on a surface which ismoving at high speed with a resulting rapid air flow over the surface.Some compounds that have been proposed to lower or depress the freezingpoint of water contacting therewith are corrosive to metal or thesurface coating of the part to be protected.

I have discovered that a compound composed of a polyhydric alcohol and apolycarboxylic acid may be formed, which serves admirably for antiicinpurposes. It is well known that glycerine, in certain proportions, maybe reacted with phthalic anhydride or other polycarboxylic acid to forma hard insoluble resin, but such a resin cannot be readily applied to asurface to be protected, and has little or no anti-icing action. Inmaking my anti-icing compound, the glycerine and phthalic anhydride arereacted under conditions and in such proportions that a somewhat stickycompound is formed in which there are free hydroxyl groups and which hasa limited amount of free glycerine.

As a preferred procedure for making the coating composition, phthalicanhydride and glycerine are mixed in substantially equal molecularproportions and are slowly heated up to about 240 C. in about forty-fiveminutes to one hour with stirring and until limited gelling occurs. Thenan additional amount of glycerine, which is preferably substantiallyequal to the original amount, is added, and the temperature is broughtup to me-Email 231301112 200 and the heatingcontinued with stirringuntil a test shows that the desired end point has been reached. l liismay beeascertained by placin a :drop iof the compound on .a clean metalsurface. The drop should be somewhat :c'loudy "but =not opaque, andsulfic'iently plastic so that-it can be smeared out with :the finger andwithout showing long stringy adherence to the finger from the metalplate. It should not be hard or brittle on becoming cold and shouldremain soft and sticky. When this end point is reached, the heat is shutoff but stirring is continued and the compound allowed to cool to aboutC., at which point ethyl alcohol or other suitable volatile thinner isadded and the stirring continued to effect a uniform dispersion. Theamount of thinner added is usually about 40 to 45% by weight of thecompound, but should be such that the compound may be readily sprayed orbrushed on the surface to be protected from icing. If the compound isapplied to the surface in a heated condition, very little, if any,thinner is needed.

The temperature of cooking may vary between about 200 C. and 280 C. andthe time of cooking may be correspondingly varied. At 200 C. thereaction is slow and requires considerable time, and at 280 C. it isvery rapid. A temperature about half way between those extremes is thepreferred one. The heating after the additional glycerine is put in,should not be substantially above 200 C. nor for a very long time.

I m not prepared to state the definite chemical composition of thecompound but it is believed to be mainly a compound of phthalicanhydride and glycerine in the ratio of about 1 mol of the former to 2mols of the latter, and thus each glycerine radical contains two free orunesterified hydroxyl groups. There should be a small amount of freeglycerine uniformly dispersed throughout the compound, but due to suchdispersion, it can be leached out by water only at a very low rate. Theproportions of the polyhydric alcohol and the polycarboxylic acid may bevaried and the amount of reaction may be controlled by varying the timeand temperature of cooking. It is important that the compound be solublein a readily volatile thinner or liquid and that after the evaporationof the thinner, the coating be somewhat sticky.

The coating acts to depressthe freezing point of water which may contactwith the treated surface, as for instance, in the form of rain, fog,mist or snow flakes, and the water having its freezing point depressedor lowered,'drains off or is thrown off if the treated surface be thatof an airplane propeller, or is blown off if the surface be some otherexposed part of an aircraft. The free glycerine is retained in thecoating for a considerable length of time under service conditions, butgradually becomes dissipated or leached out, and then a fresh coatingmay be applied directly upon the originalcoating or after Washing thelatter off by the use of a suitable solvent.

Although it is preferred that the coating contain only a relativelysmall amount of free glycerine, a very much larger amount of glycerinemay be added in preparing the compound and thus a, larger amount will bepresent in the coating. The amount should not be so large as will permitdraining of the glycerine away from the coating or the formation of acoating with is sufiiciently pre-fiowing to drain ofi the surface. In-

stead of using a single polyhydric alcohol such as the solvent.

WALTER E. PALMER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,341,735 Monsaroff Feb. 15, 19442,346,891 Adlington Apr. 18, 1944 FOREIGN PATENTS Number Country Date337,199 Great Britain Oct. 30, 1930 OTHER REFERENCES Ellis, TheChemistry of Synthetic Resins, vol.

II, 1935, pages 864 to 869.

